1. Field of Invention
This invention relates to the manufacture of an alkali metal electrochemical cell or battery, and more particularly to new and improved methods of preparing silver vanadium oxide composite cathode material for use in high energy density batteries.
2. Discussion of the Prior Art
Solid cathode, liquid organic electrolyte and alkali metal lithium anode cells or batteries are used as the power source for implantable medical devices. The cathode of such a cell may have as active material carbon fluoride, a metal oxide, a mixed metal oxide such as silver vanadium oxide, or other suitable material as disclosed in U.S. Pat. No. 4,830,940 to Keiter et al., which patent is assigned to the assignee of the present invention and is incorporated herein by reference.
Preparation of cathode material containing a mixed metal oxide such as silver vanadium oxide for use in a lithium cell or battery has been known by a decomposition reaction. However, the decomposition method of preperation is accompanied by the evolution of gaseous products. Typically, the synthesis is carried out by first thermally decomposing a vanadium salt to produce vanadium pentoxide. A decomposable metal salt, preferably containing silver, is then blended with the vanadium pentoxide in water and the mixture is oven-dried. Following drying, the mixture is again blended and ground to ensure thorough intermingling of the constituents and the resulting homogeneous mixture is subsequently baked for a final heating/decomposition period. Depending on the starting materials used, this final heating/decomposition period can result in the release of toxic by-product gases. For example, if silver nitrate (AgNO.sub.3) is used as the silver source, nitrous oxide type gases may be formed. Such a decomposition reaction for the preparation of silver vanadium oxide is: EQU AgNO.sub.3 +V.sub.2 O.sub.5 .fwdarw.AgV.sub.2 O.sub.5.5 +NO.sub.2 +1/2 SO.sub.2
Upon cooling, the baked material is blended with appropriate amounts of carbon black and graphite powder to enhance conductivity, and with a binder material, and then pressed to form the cathode. Such a method is described in more detail in U.S. Pat. No. 4,310,609 to Liang et al., which patent is assigned to the assignee of the present invention and is incorporated herein by reference.
Accordingly, the present invention provides several methods for the preparation of amorphous silver vanadium oxide by chemical addition, reaction, or otherwise intimate contact of a silver containing component preferably Ag.sub.2 O, with a vanadium-containing compound to form a mixed metal oxide bronze. The mixed metal oxide is then rendered amorphous by baking, followed by rapid cooling.
References related to the art of forming a mixed metal oxide by reacting a vanadium-containing compound with silver oxide (Ag.sub.2 O) include:
P. Fleury "Revue de Chimie minerale," 6:819-851, 1969), describes the establishment of an equilibrium diagram between liquid and solid phases of three systems formed by the solid state reaction of V.sub.2 O.sub.5 and CuO, Ag.sub.2 O and Ti.sub.2 O.sub.3, and the study of newly discovered solid phases. PA1 A. Casalot et al. "Bulletin de la Societe Chimique de Franc," 10:3817-3820, 1967), describes a study of the Ag.sub.2 O-V.sub.2 O.sub.3 -VO.sub.2 system in an alpha phase comprising a solid solution of Ag.sup.+ ions in V.sub.2 O; a monoclinic, beta phase being an isotope of homologous phases existing for the insertion of other monovalent elements, and a gamma, pseudo-orthorhombic phase. PA1 B. Rayeau "Revue de Chimie minerale", 4:735-758, 1967), describes the limited relations between the various phases of the V-Ag-O system formed under vacuum, formed in an inert atmosphere, formed in an oxygen atmosphere as well as reaction studies of oxidation and reduction in the V-Ag-0 system to show that no new phases were obtained. PA1 P. Fleury et al. "C.R. Acad. Sc. Paris," 262:475-477, 1966) describe the crystallization of melted (molten) mixtures of the Ag.sub.2 O-V.sub.2 O.sub.5 system. PA1 E. Wenda "Journal Of Thermal Analysis," 879-889, 1985), discusses phase equilibria in the V.sub.2 O.sub.5 -Ag:O system at a constant oxygen pressure (0.2 atm). The phase diagram found under these conditions was compared with the same system in vacuum and at an oxygen pressure of 1 atm in an attempt to construct the hypothetical phase diagram of V.sub.2 O-Ag.sub.2 O-O.sub.2.
Published European patent application 0 478 303 A3 discloses a cathode material for electrochemical cells of a silver vanadium oxide prepared by a chemical combination or addition reaction but the silver vanadium oxide so prepared is not amorphous.
It is, therefore, an object of this invention to provide new and improved methods for preparing a silver vanadium oxide composite cathode for use in high energy density batteries.
It is another object of the present invention to provide new and improved methods for preparing silver vanadium oxide using Ag.sub.2 O and V.sub.2 O as starting materials.
It is still another object of the present invention to provide new and improved methods for preparing silver vanadium oxide as an amorphous material.
It is a further object of this invention to provide improved chemical control for the formation of a mixed metal oxide cathode material.